Hydraulic apparatus

ABSTRACT

A hydraulic system  10  of the present invention has a hydraulic pump driven by a driving source  14 , a hydraulic pump motor  52  driven by an operating oil discharged from the hydraulic pump and flowing in an oil path  50 , an inertial body  60  connected to a rotary shaft of the hydraulic pump motor, an oil path  62  connected between an outlet port of the hydraulic pump motor and a load  22 , an unloading oil path  64  branched from the oil path  62 , and an on-off valve  68  inserted in the unloading oil path. In this configuration, as the on-off valve is opened and closed, a high pressure is generated in the oil path  62  by making use of kinetic energy of the inertial body. The inertial body is driven by hydraulic power and the inertial body is separated from the driving source, which also provides an effect of increasing degrees of freedom for an instrument layout.

TECHNICAL FIELD

The present invention relates to a hydraulic system capable ofextracting a hydraulic power greater than that generated by an oilpressure source.

BACKGROUND ART

Examples of the hydraulic systems of the above type include thosedisclosed, for example, in Japanese Patent Applications Laid-Open No.6-287952 and Laid-Open No. 2003-130006.

The hydraulic system disclosed in Japanese Patent Application Laid-OpenNo. 6-287952 relates to a press-in pile driver and is characterized inthat an unloading oil path is branched from an oil path between ahydraulic pump as an oil pressure source and a hydraulic cylinder as aload and an on-off valve is inserted in the unloading oil path. TheApplication Laid-Open No. 6-287952 describes that in this configurationthe on-off valve is instantly opened and closed to apply an oil impactto an operating oil flowing from the hydraulic pump to the hydrauliccylinder, whereupon the pressure of the operating oil can be made higherthan the discharge pressure from the hydraulic pump. However, thehydraulic system making use of the oil impact causes a considerable lossand has a limit to increase of pressure, and thus it is considered notto be practical.

In contrast to it, the hydraulic system disclosed in the ApplicationLaid-Open No. 2003-130006 is not one making use of the oil impact but isconfigured to utilize energy storage in an inertial body. Asschematically shown in FIG. 1, the hydraulic system 1 described inLaid-Open No. 2003-130006 has a hydraulic pump 4 driven by a drivingsource 3 having an inertial body 2 like a flywheel, and a load, e.g., ahydraulic motor 6 to which the operating oil discharged from thehydraulic pump 4 is supplied through an oil path 5 a. An accumulator 7is connected to the oil path 5 a and a check valve 8 is inserted in theoil path 5 a between the accumulator 7 and the hydraulic pump 4.Furthermore, an unloading oil path 5 b is branched from the oil path 5 abetween the check valve 8 and the hydraulic pump 4, and an on-off valve9 is inserted therein.

In the hydraulic system 1 of this configuration, in a state in which,while the on-off valve 9 is kept open, the hydraulic pump 4 is driven bythe driving source 3 and the operating oil is circulated from the oilpath 5 a via the unloading oil path 5 b, the outlet port of thehydraulic pump 4 is in an unloaded condition, and thus the energyoutputted from the driving source 3 is stored up as kinetic energy(½)·I·ω² of the inertial body 2, excluding losses in the hydrauliccircuit system, the mechanical system, and so on. Here I is the momentof inertia of the inertial body 2, and ω the angular velocity of theinertial body 2. When the on-off valve 9 is closed at this moment, theoperating oil discharged from the hydraulic pump 4 is supplied via thecheck valve 8 to the load 6; even if the magnitude of the load pressureafter the check valve 8 is larger than a pressure of the operating oilthat can be discharged from the hydraulic pump 4 driven by a drivetorque (Qm) as a potential output of the driving source 3, the operatingoil can be supplied at a greater pressure to the load 6 by virtue of atorque resulting from addition of a torque from the kinetic energy ofthe inertial body 2 preliminarily having stored the energy, to the drivetorque (Qm) of the driving source 3, i.e., a torque (Qp) to drive thehydraulic pump 4.

As described above, the hydraulic system 1 disclosed in Laid-Open No.2003-130006 provides the excellent effect of capability of supplying theoperating oil at the higher pressure to the load 6, but also has aproblem that usage and application ranges are limited.

For example, there are cases where the distance between the drivingsource 3 and the on-off valve 9 becomes very long because of aninstrument layout. If the range between the driving source 3 and theon-off valve 9 is arranged variable, the oil paths 5 a, 5 b between thedriving source 3 and the on-off valve 9 cannot be constructed of pipeswith high rigidity such as steel pipes, but are replaced with rubberhoses or the like in some cases. In such cases, the rubber hoses or thelike expand and contract to lower efficiency, and it is difficult toadopt the hydraulic system 1. In addition, in cases where there are aplurality of loads 6 and desires for individual control of the loads, itis necessary to prepare a plurality of hydraulic systems 1 and it isdifficult to reduce the number of parts by common use of components.

An object of the present invention is therefore to provide a hydraulicsystem making use of the energy storage in an inertial body, which canbe widely used in a variety of applications and fields.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, Inventors conducted elaborateresearch and came to note that the hydraulic system described inLaid-Open No. 2003-130006 was constructed by handling the drivingsource, the inertial body, and the hydraulic pump as an integral partand by implementing the energy storage in the inertial body bymechanical power from the driving source. Then the Inventors came todiscover separating the driving source from the inertial body. Namely,the present invention is a hydraulic system for supplying an operatingoil to a predetermined load, which comprises an oil pressure sourcecapable of outputting a predetermined hydraulic power, a first oil pathone end of which is connected to the oil pressure source, a hydraulicpump motor having an inlet port to which the other end of the first oilpath is connected, an inertial body connected to a rotary shaft of thehydraulic pump motor, a second oil path one end of which is connected toan outlet port of the hydraulic pump motor, an unloading oil pathbranched from the second oil path, an on-off valve inserted in theunloading oil path, a valve for preventing backflow of the operating oilto the unloading oil path, which is connected to the other end of thesecond oil path, and a third oil path extending from the valve andconnected to the load.

In this configuration, the hydraulic pump motor is driven by thehydraulic power outputted from the oil pressure source. This results inrotating the rotary shaft of the hydraulic pump motor and also rotatingthe inertial body connected to the hydraulic pump motor (the inertialbody encompasses an external inertial body like a flywheel and alsoencompasses an internal inertial body like a rotor of the hydraulic pumpmotor itself) to store the kinetic energy.

When the on-off valve is closed, even if the load pressure downstream ofthe check valve is higher than the discharge pressure of the oilpressure source, the energy of the inertial body is released withdecrease in the angular velocity thereof, whereby the hydraulic pumpmotor can output a pressure higher than the load pressure downstream ofthe check valve.

The on-off valve can be effectively opened and closed by use of acontroller for controlling the on-off valve, which is comprised of amicrocomputer or the like.

A typical example of the oil pressure source is considered to be ahydraulic pump driven by a driving source. In this case, where thedistance has to be set long between the driving source and the on-offvalve, the hydraulic pump motor, the on-off valve, and the check valvecan be located close to each other. Accordingly, the second oil path canbe made drastically shorter than the first oil path. This effect will bedetailed below.

Furthermore, since the hydraulic pump motor is driven by the hydraulicpower from the oil pressure source to store the energy in the inertialbody, only one oil pressure source can be shared even in a case where aplurality of loads are provided and where for each load there areprovided a hydraulic pump motor, an inertial body, a second oil path, anunloading oil path, an on-off valve, a valve for prevention of backflow,and a third oil path. Namely, the operating oil from the oil pressuresource can be distributed through branch pipes branched from the firstoil path, to the respective hydraulic pump motors, so as to enableindependent control of the individual loads.

Furthermore, the hydraulic system of the present invention preferablycomprises an accumulator connected to the third oil path. The reason isthat it becomes feasible to store and utilize the generated highpressure in the accumulator.

The above object and other features and advantages of the presentinvention will become apparent to those skilled in the art in view ofthe following detailed description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydraulic circuit diagram showing a configuration of aconventional hydraulic system.

FIG. 2 is a hydraulic circuit diagram schematically showing a wind powergenerator to which a hydraulic system according to the present inventionis applied.

FIG. 3 is a hydraulic circuit diagram showing a case where a hydraulicsystem according to the present invention is applied to a press-in piledriver.

FIG. 4 is a hydraulic circuit diagram showing a hydraulic systemaccording to the present invention in a case where there are a pluralityof loads.

FIG. 5 is a hydraulic circuit diagram showing another embodiment of ahydraulic system according to the present invention in a case wherethere are a plurality of loads.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowin detail with reference to the drawings. Identical or equivalentportions will be denoted by the same reference symbols throughout thedrawings, without redundant description.

FIG. 2 is a schematic illustration showing a wind power generator 12 towhich a hydraulic system 10 according to the present invention isapplied. The represented wind power generator 12 uses a propeller typewindmill (driving source) 14 and is arranged to once convert amechanical power generated with rotation of the windmill 14 by wind, toa hydraulic power and to thereafter convert this hydraulic power againto a mechanical power so as to rotate a rotary shaft of electricgenerator 16. For that purpose, the hydraulic system 10 in therepresented wind power generator 12 is provided with a hydraulic pump 20for converting the mechanical power to the hydraulic power, a rotaryshaft 18 of which is connected to the windmill 14, and a hydraulic pumpmotor (load) 22 for converting the hydraulic power to the mechanicalpower.

The hydraulic pump 20 is of a constant-volume one-directional rotationtype and constitutes an oil pressure source for generating the hydraulicpower in collaboration with the windmill 14. The rotary shaft 18 of thehydraulic pump 20 is rotatably supported by bearings (not shown)provided in nacelle 24, and the hydraulic pump 20 is placed in thisnacelle 24. The nacelle 24 is a box rotatably supported on an upper partof support 28 standing on foundation 26 such as the earth. An inlet port30 of the hydraulic pump 20 is communicated through an oil path 32 withan oil tank 34 placed in the nacelle 24.

The hydraulic pump motor 22 is of the constant-volume one-directionalrotation type, and is arranged to rotate its rotary shaft 40 under feedof the operating oil through its inlet port 38, to suck in the operatingoil through the inlet port 38 with rotation of the rotary shaft 40, andto discharge the operating oil from its outlet port 42. The rotary shaft40 of the hydraulic pump motor 22 is connected to a rotor 44 of theelectric generator 16.

The rotor 44 of the electric generator 16 is further coaxially connectedto a flywheel 46. The flywheel 46 is an inertial body having apredetermined inertia, also called a balance wheel, and it continues torotate by virtue of the inertia even after the input to the hydraulicpump motor 22 is shut off. The hydraulic pump motor 22, the rotor 44 ofelectric generator 16, and the flywheel 46 are connected in a state withmechanically high rigidity, but there will arise no problem even if theyare connected through a mechanism of disconnecting them by a clutch orthe like.

An oil path (first oil path) 50 is connected between an outlet port 48of the hydraulic pump 20 and an inlet port 54 of a hydraulic pump motor52. The hydraulic pump motor 52 is also of the constant-volumeone-directional rotation type as the aforementioned hydraulic pump motor22 was, and the hydraulic pump motor 52 is arranged to rotate its rotaryshaft 56 under feed of the operating oil through the inlet port 54 andis able to suck in the operating oil through the inlet port 54 withrotation of the rotary shaft 56 and to discharge the operating oil fromits outlet port 58. A flywheel 60 as an inertial body is connected tothe rotary shaft 56 of this hydraulic pump motor 52.

The outlet port 58 of the hydraulic pump motor 52 and the inlet port 38of the hydraulic pump motor 22 are in communication with each otherthrough an oil path 62. An unloading oil path 64 is branched from themiddle of the oil path 62 and is connected to an oil tank 66. An on-offvalve 68 is inserted in this unloading oil path 64. The on-off valve 68is controlled to open and close by a control signal from a controller70.

The oil path 62 is provided with a check valve 74, an accumulator 76,and an on-off valve 78, which are located in order on the downstreamside with respect to a branch point 72 of the unloading oil path 64. Thecheck valve 74 is arranged to prevent the operating oil from flowingfrom the accumulator 76 side via the unloading oil path 64 to the oiltank 66. The accumulator 76 is able to receive the operating oil fedunder pressure from the hydraulic pump motor 52 side to store energy.The on-off valve 78 is arranged to be controlled to open and close bythe controller 70.

An oil path 80 connected to an oil tank 66 is branched from the oil path62 between the on-off valve 78 and the hydraulic pump motor 22. A checkvalve 82 is inserted in this oil path 80 to prevent the operating oilfrom flowing from the oil path 62 to the oil tank 66, and with theon-off valve 78 being in a closed state, the check valve 82 permits theoperating oil to be sucked in from the oil tank 66 through the inletport 38 of the hydraulic pump motor 22.

An oil path 84 to an oil tank 66 is connected to the outlet port 42 ofthe hydraulic pump motor 22.

Here the nacelle 24 supporting the propeller type windmill 14 isdesirably as light as possible, because it horizontally rotates on theupper part of the support 28, depending upon wind directions. Inconsideration of maintenance and others, only the hydraulic pump 20 as aprincipal component is preferably disposed in the nacelle 24 and thisinevitably results in disposing the hydraulic pump motor 22, the on-offvalve 68, the check valve 74, the electric generator 16, etc. on thefoundation 26. For this reason, the oil path 50 between the on-off valve68 and, the windmill 14 and the hydraulic pump 20 in the nacelle 24 asthe oil pressure source needs to have at least a length equal to orgreater than the height of the support 28. By intensively placing thehydraulic pump motor 52, the on-off valve 68, the check valve 74, etc.and the oil paths connecting them, at appropriate positions on thefoundation 26, the branch point 72 part of the oil path 62 and theunloading oil path 64 can be shorter than the oil path 50.

In the wind power generator 12 as described above, for starting powergeneration from a windless state in which the windmill 14 is notrotated, a generation start switch (not shown) of the wind powergenerator 12 is first turned on, whereupon the controller 70 generatescontrol signals to close the on-off valve 78 and to open the on-offvalve 68. It is assumed that the oil tanks 34, 66 and all the oil pathsare filled with sufficient amount of the operating oil at the start ofpower generation and that during operation an operating oil supply (notshown) properly supplies the operating oil so as to avoid vacancy of theoil tank 34.

As wind starts blowing to rotate the windmill 14 and rotate the rotaryshaft 18 of the hydraulic pump 20, the operating oil is sucked from theoil tank 34 into the hydraulic pump 20 and is discharged therefrom. Thenthe operating oil passes through the oil path 50 to flow into the inletport 54 of the hydraulic pump motor 52 to rotate the rotary shaft 56 ofthe hydraulic pump motor 52. On this occasion, the operating oil flowsout of the outlet port 58 of the hydraulic pump motor 52 and then flowsfrom the oil path 62 through the unloading oil path 64 into the oil tank66. Since the on-off valve 68 in the unloading oil path 64 is in an openstate, the load on the hydraulic pump 20 and on the hydraulic pump motor52 is smaller than during power generation, and the windmill 14 isreadily accelerated by that degree. The rotation of the flywheel 60connected to the rotary shaft 56 of the hydraulic pump motor 52 is alsoaccelerated with the acceleration of the windmill 14 to store energy.

Thereafter, the controller 70 issues a control signal to the on-offvalve 68 to switch it into a closed state, whereupon the operating oildischarged from the hydraulic pump motor 52 flows into the accumulator76 to be accumulated. On this occasion, a torque generated by thehydraulic power fed to the inlet port 54 and the kinetic energy storedin the flywheel 60 is applied to the hydraulic pump motor 52, and a highpressure over the discharge pressure of the hydraulic pump 20 driven bythe torque outputted from the driving source is generated according tothe load pressure on the downstream side of the check valve 74, in theoil path 62 between the outlet port 58 of the hydraulic pump motor 52and the check valve 74 and in the unloading oil path 64 from the branchpoint 72 to the on-off valve 68. In other words, if the load pressuredownstream of the check valve 74 is higher than the discharge pressureof the hydraulic pump 20, the windmill (driving source) 14 driving thehydraulic pump 20 cannot maintain its rotation under ordinarycircumstances. However, the shortage is compensated for by a torquegenerated from the kinetic energy of the inertial body 60 connected tothe hydraulic pump motor 52, whereby the hydraulic pump motor 52generates the discharge pressure enough to feed the operating oilagainst the high load pressure. Then the opening and closing operationsof the on-off valve 68 are repeated (or switched) at appropriatetimings, whereupon the operating oil at high pressure is continuouslyfed into the accumulator 76 to raise the pressure in the accumulator 76,in combination with the closing of the on-off valve 78.

Let us suppose herein that while the windmill 14 is rotating at aconstant speed, the torque outputted by the windmill 14 is denoted byQm. The hydraulic pump motor 52 is driven by the hydraulic power fromthe hydraulic pump 20 driven by this drive torque (Qm). It can be easilyunderstood that, where Qp stands for the drive torque generated by thehydraulic pump motor 52, Qp=Qm, provided that the on-off valve 68 is inan open state and the losses in the hydraulic circuit system, themechanical system, etc. are ignored. On the other hand, the energyoutputted from the hydraulic pump motor 52 is stored as the kineticenergy (½)·I·ω² of the flywheel 60. When the on-off valve 68 is switchedinto a closed state, the hydraulic pump motor 52 is subjected to a load,whereby the amount of oil from the hydraulic pump 20 is reduced and therotational speed of the rotary shaft 56 of the hydraulic pump motor 52is reduced. However, since the inertial torque of the flywheel 60,I·dω/dt, is added, the relation of Qp=Qm−I·dω/dt holds, so that thedischarge pressure of the hydraulic pump motor 52 increases according tothe load pressure. This relation is equivalent to that in theconventional configuration wherein the hydraulic pump, the inertialbody, and the driving source are integrated (cf. FIG. 1).

Incidentally, the branch point 72 part of the oil path 62 and theunloading oil path 64 are short and can be constructed of pipes withhigh rigidity such as steel pipes, as described above. Therefore, evenif there occur such pressures as repetitions of high and low pressuresby the switching control of on and off of the on-off valve 68, lossesdue to expansion and contraction of the pipe paths and frictional lossesof the pipe paths can be reduced to the extent that the branch point 72part of the oil path 62 and the unloading oil path 64 are shorter.Accordingly, energy is accumulated at a desired high pressure in theaccumulator 76. On the other hand, only the discharge pressure of thehydraulic pump 20 acts on the oil path 50.

This discharge pressure can be assumed to become maximum at the maximumwind speed of wind on the windmill 14 from the viewpoint that the windenergy is high at that moment, but even the maximum discharge pressureis lower than the pressure that can be generated in the oil path 62 orthe like. It is also possible to perform a control to generate only alow pressure. In terms of the magnitude of the moment of inertia of thewindmill 14, the fluctuation velocity of the discharge pressure issmaller than the fluctuation velocity of fluctuations of the pressurecaused by the switching control to open and close the on-off valve 68and the on-off valve 78. The pulsation of the discharge pressureoutputted from the hydraulic pump motor 52, which is caused by switchingof the on-off valve 68, does not affect the upstream of the hydraulicpump motor 52, i.e., the oil path 50. Therefore, even in cases where theoil path 50 is longer than the oil path of the branch point 72 part orwhere the oil path is constructed of a rubber hose or the like, theexpansion and contraction of the tube path is small and a drop ofefficiency due to repetition of expansion and contraction is extremelysmall.

When the pressure of the accumulator 76 reaches a predetermined value,the on-off valve 78 is opened, whereupon the operating oil flows throughthe oil path 62 to the hydraulic pump motor 22. As the operating oil issupplied to the hydraulic pump motor 22, the rotary shaft 40 of thehydraulic pump motor 22 rotates to rotate the rotor 44 of the electricgenerator 16. Even if the pressure (load pressure) necessary for drivingof the hydraulic pump motor 22 is higher than the discharge pressure ofthe hydraulic pump 20, the high pressure can be generated from thehydraulic pump motor 52 by use of the kinetic energy of the flywheel 60as described above. Therefore, by preliminarily determining the kineticenergy of the flywheel 60 according to the load pressure, it alsobecomes feasible to drive the hydraulic pump motor 22. As the hydraulicpump motor 22 is driven in this manner to drive the electric generator16, power generation is started.

Since the hydraulic pump motor 52 with inertia is placed between theon-off valve 68 and the hydraulic pump 20 and in the vicinity of theon-off valve 68, as described above, the high pressure can beefficiently extracted even in cases where the distance is long betweenthe windmill 14 for driving the hydraulic pump 20, i.e., the drivingsource, and the on-off valve 68 or where the oil path of a rubber hoseor the like needs to be used there, because of the layout. Thishydraulic pump motor 52 functions like a capacitor in an electriccircuit wherein the capacitor is disposed in the vicinity of a load tosupply a stable voltage to the load where the distance is long between apower supply and the load.

An effective way is such that the controller 70 automatically controlsthe on-off valves 68, 78, based on signals from a pressure sensor 88 fordetecting the pressure in the accumulator 76, an unrepresentedrevolution meter for detecting the number of revolutions of the flywheel60, and so on. In FIG. 2, the sensor, an oil path 90 to communicate theinlet port 54 of the hydraulic pump motor 52 with an oil tank 66, and acheck valve 92 inserted therein are provided for continuously supplyingthe operating oil to the hydraulic pump motor 52 to assure continuouspower generation even if the rotation of the windmill 14 stops duringrotation of the inertial body 60.

The preferred embodiment of the present invention was described above indetail, but the present invention is not limited to the aboveembodiment. For example, the above embodiment is an application of thepresent invention to the wind power generator, and the hydraulic systemof the present invention can also be commonly applied to otherapplications; in such cases the load to which the operating oil issupplied can be one except for the hydraulic pump motor.

For example, as shown in FIG. 3, the present invention can beeffectively applied to a press-in pile driver. In the case of the piledriver, a hydraulic cylinder (load) 122 for driving a pile 100 issometimes far from a driving source 114 such as an electric motor or aninternal combustion engine, but the hydraulic pump motor 52, the on-offvalve 68, the check valve 74, the accumulator 76, etc. can be disposedin the vicinity of the hydraulic cylinder 122, as described above.

Where there are a plurality of loads to be individually controlled(e.g., a hydraulic cylinder for mold clamping, a hydraulic cylinder forsupply of molten resin, etc. in one injection molding machine), aconfiguration as shown in FIG. 4 can be adopted. As seen from FIG. 4,there is only one oil pressure source, i.e., a driving source 214 and ahydraulic pump 20 for a plurality of loads 222 a, 222 b, 222 c, . . . Ahydraulic pump motor 52 with a flywheel 60 and components thereafter areprovided for each of the loads 222 a, 222 b, 222 c, . . .

In this configuration, the hydraulic power from the oil pressure source214, 20 is distributed to the hydraulic pump motors 52 throughrespective branch oil paths 250 a, 250 b, 250 c, . . . branched from anoil path 50. After the hydraulic pump motors 52 are driven by thedistributed hydraulic power, hydraulic circuits associated with therespective hydraulic pump motors 52 are controlled independently of eachother to enable hydraulic control of driving of the associated loads 222a, 222 b, 222 c, . . . Since this configuration requires only onedriving source 214, the installation space for the driving source can bereduced, which provides the effect of expanding the applicability of thepresent invention.

The system may also be effectively so arranged, as shown in FIG. 4, thatan on-off valve 251 is inserted in each of the branch oil paths 250 a,250 b, 250 c, . . . and that the on-off valves are individuallycontrolled to control supply and stop of the operating oil to therespective hydraulic pump motors 52. In this configuration, in order tomaintain the rotation of the inertial body 60 at the associatedhydraulic pump motor 52 even with one of the on-off valves 251 beingclosed, an oil path 290 with a check valve 292 is preferably connectedto an inlet port of each hydraulic pump motor 52 so as to supply theoperating oil to each hydraulic pump motor 52.

Furthermore, another conceivable configuration with a plurality of loadsis one as shown in FIG. 5. In this configuration, hydraulic pump motors352 a, 352 b are arranged as many as loads 222 a, 222 b, but there isonly one flywheel 360 as an inertial body shared by the both hydraulicpump motors 352 a, 352 b. In this configuration, the loads 222 a, 222 bcan also be individually controlled. The hydraulic pump motors 352 a,352 b constitute a so-called flow divider 300. Namely, the hydraulicpump motors 352 a, 352 b are coupled by a common rotary shaft, and whenthe operating oil flows from the hydraulic pump 20 into each of thehydraulic pump motors 352 a, 352 b, they are rotated at the same numberof revolutions and thus the operating oil flows at the same flow rateout of each of the hydraulic pump motors 352 a, 352 b.

Furthermore, it is also possible to adopt a configuration for deliveringthe generated high pressure to the load, without provision of theaccumulator.

INDUSTRIAL APPLICABILITY

As described above, the present invention provides the effect ofachieving high hydraulic efficiency, similar to that by the hydraulicsystem disclosed in Laid-Open No. 2003-130006, and also provides theeffect of increasing degrees of freedom for the instrument layout as aresult of using the hydraulic power as the power for rotating theinertial body and separating the inertial body from the driving source.

The present invention also enables driving of multiple loads by onedriving source. Therefore, the scope of application and usage of thehydraulic system of the present invention is dramatically expanded incomparison with the conventional similar apparatus, thereby contributingto industrial growth.

1. A hydraulic system for supplying an operating oil to a predeterminedload, comprising: an oil pressure source capable of outputting apredetermined hydraulic power; a first oil path one end of which isconnected to the oil pressure source; a hydraulic pump motor having aninlet port to which the other end of the first oil path is connected; aninertial body connected to a rotary shaft of the hydraulic pump motor; asecond oil path one end of which is connected to an outlet port of thehydraulic pump motor; an unloading oil path branched from the second oilpath; an on-off valve inserted in the unloading oil path; a valve forpreventing backflow of the operating oil to the unloading oil path,which is connected to the other end of the second oil path; and a thirdoil path extending from the valve and connected to the load.
 2. Thehydraulic system according to claim 1, further comprising a controllerfor controlling opening and closing of the on-off valve.
 3. Thehydraulic system according to claim 1, wherein the oil pressure sourceis a hydraulic pump driven by a driving source.
 4. The hydraulic systemaccording to claim 1, wherein the load comprises a plurality of loads,wherein there are the hydraulic pump motor, the inertial body, thesecond oil path, the unloading oil path, the on-off valve, the valve forpreventing backflow, and the third oil path provided for each of theplurality of loads, and wherein the oil pressure source comprises onlyone oil pressure source provided for the plurality of loads, and thefirst oil path is branched into oil paths as many as the loads, to beconnected to inlet ports of the corresponding hydraulic pump motors.